This invention relates to color picture tubes and particularly to such tubes having a slit type apertured shadow mask.
Shadow mask type color picture tubes usually include a screen of red, green and blue emitting phosphor lines or dots, electron gun means for exciting the screen and a shadow mask interposed between the gun means and the screen. The shadow mask is a thin multiapertured sheet of metal precisely disposed adjacent the screen so that the mask apertures are systematically related to the phosphor lines or dots.
Color picture tubes having shadow masks with slit shaped apertures have received relatively recent commercial acceptance. One of the reasons for this acceptance is that the percentage of electron beam transmission through the mask can be made higher for a slit mask, line screen type of tube than for a circular apertured mask, dot screen type tube. Even though the use of a slit mask provides a definite advantage in electron beam transmission, the percentage of electron beam transmission through a slit mask can be increased even further than is practiced in the present art.
In one type of slit shadow mask, the mask has vertically extending slit apertures which are interrupted by a plurality of spaced bridges or webs which provide mechanical rigidity. The presence of these webs, however, reduces electron beam transmission and thus also reduces luminescent brightness. On the other hand, the webs serve the useful function of providing mechanical strength to the mask during its formation into a domed shape. Thus because of the desirability of both increased electron beam transmission and mask strength, the web shape and/or size is usually a compromise between both of these factors. A problem therefore exists of how to increase electron beam transmission without affecting the mechanical strength needed for mask formation and subsequent handling.